Sprint on Tuesday joined the roster of U.S. carriers offering rollover data for prepaid cellular plans, but with some key restrictions, according to an official announcement.

Beginning immediately, the Sprint Monthly Rolling Data feature applies to any prepaid plan costing at least $35 a month, and offers a 30-gigabyte cap with no expiration date for the rolled-over data.

In comparison, Rollover Data from AT&T GoPhone requires people to spend at least $45 per month, and has a 30-day expiration window. T-Mobile's Data Stash demands that subscribers have a $60 plan, but with a 12-month time limit.

To qualify for the Sprint option, however, people must subscribe through Best Buy. The carrier also stated on Tuesday that Monthly Rolling Data is a "limited time" offer, though there's no indication of when it might end.